Field of the Invention
The present invention relates to a one-time memory control apparatus suitable for a vehicle LSI (semiconductor integrated circuit) utilizing built-in fuses.
Description of the Related Art
As a means for writing and retaining inherent information items such as setting values at a time when an LSI is shipped, a one-time memory such as a fuse is utilized. The logic for the state of information to be retained in the one-time memory is determined by the closing state of the fuse. However, there has been a problem that due to thermal expansion, distortion caused by a stress, or the like, a fuse that has been opened is closed again and hence an accidental logic conversion occurs. Moreover, there has been a problem that a fuse that has not been opened is opened due to a disturbance such as noise and hence an accidental logic conversion occurs.
For example, in the state determination method for a semiconductor device and a fuse circuit disclosed in Patent Document 1, two or more fuses are multiplexed and a fuse logic is determined through a logical sum, so that contact between opened surfaces that have been opened at a time of opening of a fuse is prevented from causing an accidental logic conversion. In the semiconductor device disclosed in Patent Document 2, a fuse writing enable signal itself for controlling a fuse opening current is nullified, so that erroneous opening of a fuse at a time when the fuse is not to be opened is prevented from causing an accidental logic conversion.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-210316    [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-97696
However, in the case of Patent Document 1, there has been a problem that although in the case where a fuse that has been opened is closed, an accidental logic conversion can be prevented through multiplexing, a fuse cannot be prevented from being opened by a fuse opening current that erroneously flows. Moreover, in the case of Patent Document 2, there has been a problem that although there is provided a fuse for prohibiting the operation of a fuse opening current creation circuit, the reliability is low because multiplexing of a fuse is not implemented.